Offset lithography is a common method of printing today. (For the purposes hereof, the terms “printing” and “marking” are interchangeable.) In a typical lithographic process, an image transfer element or imaging plate, which may be a flat plate-like structure, the surface of a cylinder, or belt, etc., is configured to have “image regions” formed of hydrophobic and oleophilic material, and “non-image regions” formed of a hydrophilic material. The image regions are regions corresponding to the areas on the final print (i.e., the target substrate) that are occupied by a printing or marking material such as ink, whereas the non-image regions are the regions corresponding to the areas on the final print that are not occupied by said marking material. The hydrophilic regions accept and are readily wetted by a water-based fluid, commonly referred to as a fountain solution or dampening fluid (typically consisting of water and a small amount of alcohol as well as other additives and/or surfactants to, for example, reduce surface tension). The hydrophobic regions repel fountain solution and accept ink, whereas the fountain solution formed over the hydrophilic regions forms a fluid “release layer” for rejecting ink. Therefore, the hydrophilic regions of the imaging plate correspond to unprinted areas, or “non-image areas”, of the final print.
The ink may be transferred directly to a substrate, such as paper, or may be applied to an intermediate surface, such as an offset (or blanket) cylinder in an offset printing system. In the latter case, the offset cylinder is covered with a conformable coating or sleeve with a surface that can conform to the texture of the substrate, which may have surface peak-to-valley depth somewhat greater than the surface peak-to-valley depth of the imaging blanket. Sufficient pressure is used to transfer the image from the blanket or offset cylinder to the substrate.
The above-described lithographic and offset printing techniques utilize plates which are permanently patterned with the image to be printed (or its negative), and are therefore useful only when printing a large number of copies of the same image (long print runs), such as magazines, newspapers, and the like. These methods do not permit printing a different pattern from one page to the next (referred to herein as variable printing) without removing and replacing the print cylinder and/or the imaging plate (i.e., the technique cannot accommodate true high speed variable printing wherein the image changes from impression to impression, for example, as in the case of digital printing systems).
Efforts have been made to create lithographic and offset printing systems for variable data. One example is disclosed in U.S. Patent Application Publication No. 2012/0103212 A1 (the '212 Publication) published May 3, 2012, and based on U.S. patent application Ser. No. 13/095,714, which is commonly assigned, and the disclosure of which is hereby incorporated by reference herein in its entirety, in which an intense energy source such as a laser is used to pattern-wise evaporate a fountain solution. The '212 publication discloses a family of variable data lithography devices that use a structure to perform both the functions of a traditional imaging plate and of a traditional blanket to retain a patterned fountain solution of dampening fluid for inking, and to delivering that ink pattern to a substrate. A blanket performing both of these functions is referred to herein as an imaging blanket. The imaging blanket retains a fountain solution, requiring that its surface have a selected texture.
Fluoroelastomers and fluoropolymers have been used in a variety of printing systems over the years. For example, fluoroelastomers have been used to form the reimageable surface layer in variable data lithography systems. Such reimageable surface layers have included Trifluorotoluene (TFT) as a solvent. However, the inventors found that TFT is not an environmentally friendly solvent and therefore is not manufacture friendly. Further, known crosslinkers such as XL-150 (available from Nusil) are expensive and, thus, undesirable. Also, the current formulations require vigorous shaking with a paint shaker for long hours (e.g., 6-8 hours) to disperse the carbon black in the formulation. Thus, a benefit could be provided by the development of a reimageable surface layer formulation with an environmentally friendly solvent and a crosslinking system that enables a scale-up process for manufacture. It would also be beneficial to provide a more manufacture friendly way of preparing the formulation.